Note: In the present specification, the word resin has been used with two meanings customary in the art. The first meaning refers to a composition that is injected into a liquid injection molding apparatus and is very broad with respect to the chemical composition of its component parts. The second meaning is more specific to the chemistry of organopolysiloxanes and related silicone polymers, referring there to MQ, MDQ, MTQ, or MDTQ and similar compositions that may or may not comprise a precursor feedstock to a liquid injection molding apparatus.
Liquid injection moldable organopolysiloxane compositions are known and used. A problem with all such compositions is that the hardness, tensile strength, elongation and tear are so interdependent among themselves and also with the viscosity of the uncured liquid precursor that it is difficult to improve one property without deleterious effects on the other properties. Additionally, the kinetics and thermochemistry of the liquid injection molding process and the compositions used therewith have been such that only small lightweight articles of manufacture could be made by the techniques of liquid injection molding because of the speed with which the liquid precursor cures once it has been injected into the mold.
Liquid injection molding organopolysiloxane compositions are typically provided as two components that are mixed immediately prior to use. Both components contain alkenyl polymers, fillers, and in some cases resins. The first component contains a platinum catalyst while the second component contains a hydride cross linker and cure inhibitors. The two components are mixed immediately prior to use in the injection molding apparatus. In addition to providing a so-called formulation pot-life, the inhibitor must prevent curing of the curable composition until the mold is completely filled. Once the mold is completely filled the inhibitor must then allow for a rapid cure of the curable or polymerizable composition in order to ensure a short cycle life.
U.S. Pat. Nos. 3,884,866 and 3,957,713 describe high strength addition cured compositions suitable for low pressure liquid injection molding. These compositions comprise a first component containing a high viscosity vinyl end-stopped organopolysiloxane, a low viscosity vinyl containing organopolysiloxane, filler, and platinum catalyst which is cured by mixing with a second component containing a hydrogen silicone composition. This composition has a low durometer, ca 20-35 Shore A, and, moreover it is difficult to increase the durometer or hardness without adversely affecting other properties.
U.S. Pat. No. 4,162,243 discloses compositions similar to the previously referenced compositions but they contain as the most important distinction, fumed silica that has been treated with hexamethyidisilazane and tetramethyldivinyidisilazane. The compositions of the '243 patent cure to elastomers having high hardness with good retention of other properties including strength, elongation, and tear in addition to having a low viscosity in the uncured state.
U.S. Pat. No. 4,427,801 extends the teaching of the '243 patent by incorporating a MM.sup.Vi Q resin in addition to the vinyl containing treated fumed silica. This produces elastomers having even a higher hardness and tear strength but has the disadvantage of higher compression set and lower Bashore resilience.
It is an object of the present invention to produce a liquid injection molding organopolysiloxane composition having high hardness and tear strengths without resultant adverse effects on other physical properties, such a composition being particularly suited to the injection molding of large silicone rubber articles.
It is an additional object of the present invention to produce curable liquid injection molding compositions preferably organopolysiloxane compositions that additionally have good shelf stability and good mold release, and may be employed in the manufacture of large silicone rubber articles.
The manufacturing technique of liquid injection molding typically has been liquid injection moldingited to small parts, usually materials weighing less than from about 5 to about 50 grams. Advances in technology are allowing liquid injection molded parts to become larger. Larger parts require larger molds. Larger molds require more time to fill the mold with resin and thus curing must be inhibited for longer times in order to allow the mold to fill before cure may be initiated.
It is an additional object of the present invention to provide novel liquid injection molding inhibitors that will allow the manufacture of larger articles of manufacture than heretofore were possible to be made from curable liquid organopolysiloxane compositions or other curable resins.
It is an additional object of the present invention to provide articles of manufacture manufactured using curable liquid injection molding resins containing the injection molding inhibitors of the present invention or mixtures comprising said injection molding inhibitor compounds wherein said inhibitor compounds cure into the curable resin forming chemical bonds between the injection molding inhibitor compounds of the present invention and the curable resin thereby forming an article of manufacture manufactured from a new composition of matter.
These and other objects will become apparent to those skilled in the art upon consideration of the present specification, examples, and claims.